Water-Sensitive Film Containing an Olefinic Elastomer

ABSTRACT

A film that is both elastic and water-sensitive (e.g., water-soluble, water-dispersible, etc.) in that it loses its integrity over time in the presence of water is provided. To achieve these dual attributes, the film contains an olefinic elastomer and a water-soluble polymer. Although these polymers are normally chemically incompatible due to their different polarities, the present inventors have discovered that phase separation may be minimized by selectively controlling certain aspects of the film, such as the nature of the polyolefin, water-soluble polymer, and other film components, the relative amount of the film components, and so forth. For example, certain water-soluble polymers may be selected that have a low molecular weight and viscosity to enhance their melt compatibility with nonpolar polyolefins. This, in turn, may result in a film that is generally free of separate phases, which would otherwise limit the ability of the water-soluble polymer to contact water and disperse.

BACKGROUND OF THE INVENTION

Films are employed in a wide variety of disposable goods, such asdiapers, sanitary napkins, adult incontinence garments, bandages, etc.For example, many sanitary napkins have an adhesive strip on thebackside of the napkin (the napkin surface opposite to thebody-contacting surface) to affix the napkin to an undergarment and holdthe napkin in place against the body. Before use, the adhesive strip isprotected with a peelable release liner. Once removed, the peelablerelease liner must be discarded. Conventional release liners may containa film or paper coated with a release coating. Such release-coated filmsor papers, however, do not readily disperse in water, and as such,disposal options are limited to depositing the release liner in a trashreceptacle. Although disposing of conventional release liners in atoilet would be convenient to the consumer, it would potentially createblockages in the toilet.

Flushable films have been developed that are formed from awater-dispersible polymer. U.S. Pat. No. 6,296,914 to Kerins, et al.describes a water-sensitive film that may include, for instance,polyethylene oxide, ethylene oxide-propylene oxide copolymers,polymethacrylic acid, polymethacrylic acid copolymers, polyvinylalcohol, poly(2-ethyl oxazoline), polyvinyl methyl ether, polyvinylpyrrolidone/vinyl acetate copolymers, methyl cellulose, ethyl cellulose,hydroxypropyl cellulose, hydroxypropyl methyl cellulose, ethylhydroxyethyl cellulose, methyl ether starch, poly (n-isopropylacrylamide), poly N-vinyl caprolactam, polyvinyl methyl oxazolidone,poly (2-isopropyl-2-oxazoline), poly (2,4-dimethyl-6-triazinylethylene), or a combination thereof. Some of these polymers, however,are not thermoplastic and thus are not readily processed usingthermoplastic film converting equipment. Further, these films are alsonot elastic and may thus be limited in their use. In response to theseand other problems, attempts have been made to form water-shrinkablefilms from elastomeric and water-dispersible polymers. One such film isdescribed in U.S. Pat. No. 5,641,562 to Larson, et al. In one example,the film is formed that contains polyethylene oxide having a molecularweight of about 200,000 and an ethylene vinyl acetate copolymer.Although such films are shrinkable, they nevertheless are notdispersible or disintegratable in water so as to achieve completeflushability. Furthermore the films are not elastic.

As such, a need currently exists for an improved film that is bothelastic and water-sensitive in that it readily loses its integrity overtime in the presence of water.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, awater-sensitive elastic film is disclosed that comprises at least onewater-soluble polymer, at least one plasticizer, and at least oneolefinic elastomer. The water-soluble polymer has a weight averagemolecular weight of from about 10,000 to about 150,000 grams per moleand a number average molecular weight of from about 1,000 to about80,000 grams per mole. The weight ratio of the water-soluble polymer tothe plasticizer is from about 1 to about 50 and the weight ratio of thewater-soluble polymer to the polyolefin is from about 0.01 to about 3.0.

In accordance with another embodiment of the present invention, a methodfor forming a water-sensitive, elastic film is disclosed. The methodcomprises melt blending a composition that comprises at least onewater-soluble polymer, at least one plasticizer, and at least oneolefinic elastomer. The method also comprises extruding the compositionto form a film.

Other features and aspects of the present invention are discussed ingreater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth more particularly in the remainder of the specification, whichmakes reference to the appended figures in which:

FIG. 1 is a schematic illustration of one embodiment of a method forforming a film in accordance with the present invention;

FIG. 2 is a top view of an absorbent article that may be formed inaccordance with one embodiment of the present invention;

FIG. 3 is a graph showing the melt viscosity of plasticized Elvanol™51-05, Celvol™ 523S, and Vistamaxx™ 1120 at various shear rates;

FIG. 4 is an SEM photograph of the film of Example 6; and

FIG. 5 is an SEM photograph of the film of Example 7.

Repeat use of references characters in the present specification anddrawings is intended to represent same or analogous features or elementsof the invention.

DETAILED DESCRIPTION OF REPRESENTATIVE EMBODIMENTS DEFINITIONS

As used herein, the terms “machine direction” or “MD” generally refersto the direction in which a material is produced. The term“cross-machine direction” or “CD” refers to the direction perpendicularto the machine direction. Dimensions measured in the cross-machinedirection are referred to as “width” dimension, while dimensionsmeasured in the machine direction are referred to as “length”dimensions.

As used herein, the term “elastomeric” and “elastic” and refers to amaterial that, upon application of a stretching force, is stretchable inat least one direction (such as the CD direction), and which uponrelease of the stretching force, contracts/returns to approximately itsoriginal dimension. For example, a stretched material may have astretched length that is at least 50% greater than its relaxedunstretched length, and which will recover to within at least 50% of itsstretched length upon release of the stretching force. A hypotheticalexample would be a one (1) inch sample of a material that is stretchableto at least 1.50 inches and which, upon release of the stretching force,will recover to a length of at least 1.25 inches. Desirably, thematerial contracts or recovers at least 50%, and even more desirably, atleast 80% of the stretched length.

As used herein the terms “extensible” or “extensibility” generallyrefers to a material that stretches or extends in the direction of anapplied force by at least about 50% of its relaxed length or width. Anextensible material does not necessarily have recovery properties. Forexample, an elastomeric material is an extensible material havingrecovery properties. A film may be extensible, but not have recoveryproperties, and thus, be an extensible, non-elastic material.

As used herein, the term “percent stretch” refers to the degree to whicha material stretches in a given direction when subjected to a certainforce. In particular, percent stretch is determined by measuring theincrease in length of the material in the stretched dimension, dividingthat value by the original dimension of the material, and thenmultiplying by 100.

As used herein, the term “set” refers to retained elongation in amaterial sample following the elongation and recovery, i.e., after thematerial has been stretched and allowed to relax during a cycle test.

As used herein, the term “percent set” is the measure of the amount ofthe material stretched from its original length after being stretchedand relaxed. The remaining strain after the removal of the appliedstress is measured as the percent set.

DETAILED DESCRIPTION

Reference now will be made in detail to various embodiments of theinvention, one or more examples of which are set forth below. Eachexample is provided by way of explanation of the invention, notlimitation of the invention. In fact, it will be apparent to thoseskilled in the art that various modifications and variations may be madein the present invention without departing from the scope or spirit ofthe invention. For instance, features illustrated or described as partof one embodiment, may be used on another embodiment to yield a stillfurther embodiment. Thus, it is intended that the present inventioncovers such modifications and variations as come within the scope of theappended claims and their equivalents.

Generally speaking, the present invention is directed to a film that isboth elastic and water-sensitive (e.g., water-soluble,water-dispersible, etc.) in that it loses its integrity over time in thepresence of water. To achieve these dual attributes, the film containsan olefinic elastomer and a water-soluble polymer. Although thesepolymers are normally chemically incompatible due to their differentpolarities, the present inventors have discovered that phase separationmay be minimized by selectively controlling certain aspects of the film,such as the nature of the polyolefin, water-soluble polymer, and otherfilm components, the relative amount of the film components, and soforth. For example, certain water-soluble polymers may be selected thathave a low molecular weight and viscosity to enhance their meltcompatibility with nonpolar polyolefins. This, in turn, may result in afilm that is generally free of separate phases, which would otherwiselimit the ability of the water-soluble polymer to contact water anddisperse. In this regard, various embodiments of the present inventionwill now be described in more detail below.

I. Film Components

A. Olefinic Elastomer

Various olefinic elastomers may be employed in the film as is known inthe art. In one embodiment, for example, the olefinic elastomer is apolyolefin that has or is capable of exhibiting a substantially regularstructure (“semi-crystalline”). Such olefinic elastomers may besubstantially amorphous in their undeformed state, but form crystallinedomains upon stretching. The degree of crystallinity of the olefinpolymer may be from about 3% to about 30%, in some embodiments fromabout 5% to about 25%, and in some embodiments, from about 5% and about15%. Likewise, the olefinic elastomer may have a latent heat of fusion(ΔH_(f)), which is another indicator of the degree of crystallinity, offrom about 15 to about 75 Joules per gram (“J/g”), in some embodimentsfrom about 20 to about 65 J/g, and in some embodiments, from 25 to about50 J/g. The olefinic elastomer may also have a Vicat softeningtemperature of from about 10° C. to about 100° C., in some embodimentsfrom about 20° C. to about 80° C., and in some embodiments, from about30° C. to about 60° C. The olefinic elastomer may have a meltingtemperature of from about 20° C. to about 120° C., in some embodimentsfrom about 35° C. to about 90° C., and in some embodiments, from about40° C. to about 80° C. The latent heat of fusion (ΔH_(f)) and meltingtemperature may be determined using differential scanning calorimetry(“DSC”) in accordance with ASTM D-3417 as is well known to those skilledin the art. The Vicat softening temperature may be determined inaccordance with ASTM D-1525.

Exemplary semi-crystalline olefinic elastomers include polyethylene,polypropylene, blends and copolymers thereof. In one particularembodiment, a polyethylene is employed that is a copolymer of ethyleneand an α-olefin, such as a C₃-C₂₀ α-olefin or C₃-C₁₂ α-olefin. Suitableα-olefins may be linear or branched (e.g., one or more C₁-C₃ alkylbranches, or an aryl group). Specific examples include 1-butene;3-methyl-1-butene; 3,3-dimethyl-1-butene; 1-pentene; 1-pentene with oneor more methyl, ethyl or propyl substituents; 1-hexene with one or moremethyl, ethyl or propyl substituents; 1-heptene with one or more methyl,ethyl or propyl substituents; 1-octene with one or more methyl, ethyl orpropyl substituents; 1-nonene with one or more methyl, ethyl or propylsubstituents; ethyl, methyl or dimethyl-substituted 1-decene;1-dodecene; and styrene. Particularly desired α-olefin comonomers are1-butene, 1-hexene and 1-octene. The ethylene content of such copolymersmay be from about 60 mole % to about 99 mole %, in some embodiments fromabout 80 mole % to about 98.5 mole %, and in some embodiments, fromabout 87 mole % to about 97.5 mole %. The α-olefin content may likewiserange from about 1 mole % to about 40 mole %, in some embodiments fromabout 1.5 mole % to about 15 mole %, and in some embodiments, from about2.5 mole % to about 13 mole %. Propylene polymers may also be suitablefor use as an olefinic elastomer. In one particular embodiment, thesemi-crystalline propylene-based polymer includes a copolymer ofpropylene and an α-olefin, such as a C₂-C₂₀ α-olefin or C₂-C₁₂ α-olefin.Particularly desired α-olefin comonomers are ethylene, 1-butene,1-hexene and 1-octene. The propylene content of such copolymers may befrom about 60 mole % to about 99.5 wt. %, in some embodiments from about80 mole % to about 99 mole %, and in some embodiments, from about 85mole % to about 98 mole %. The α-olefin content may likewise range fromabout 0.5 mole % to about 40 mole %, in some embodiments from about 1mole % to about 20 mole %, and in some embodiments, from about 2 mole %to about 15 mole %.

Any of a variety of known techniques may generally be employed to formthe olefinic elastomers. For instance, olefin polymers may be formedusing a free radical or a coordination catalyst (e.g., Ziegler-Natta).Preferably, the olefin polymer is formed from a single-site coordinationcatalyst, such as a metallocene catalyst. Such a catalyst systemproduces ethylene copolymers in which the comonomer is randomlydistributed within a molecular chain and uniformly distributed acrossthe different molecular weight fractions. Metallocene-catalyzedpolyolefins are described, for instance, in U.S. Pat. No. 5,571,619 toMcAlpin et al.; U.S. Pat. No. 5,322,728 to Davis et al.; U.S. Pat. No.5,472,775 to Obioeski et al.; U.S. Pat. No. 5,272,236 to Lai et al.; andU.S. Pat. No. 6,090,325 to Wheat, et al., which are incorporated hereinin their entirety by reference thereto for all purposes. Examples ofmetallocene catalysts include bis(n-butylcyclopentadienyl)titaniumdichloride, bis(n-butylcyclopentadienyl)zirconium dichloride,bis(cyclopentadienyl)scandium chloride, bis(indenyl)zirconiumdichloride, bis(methylcyclopentadienyl)titanium dichloride,bis(methylcyclopentadienyl)zirconium dichloride, cobaltocene,cyclopentadienyltitanium trichloride, ferrocene, hafnocene dichloride,isopropyl(cyclopentadienyl,-1-flourenyl)zirconium dichloride,molybdocene dichloride, nickelocene, niobocene dichloride, ruthenocene,titanocene dichloride, zirconocene chloride hydride, zirconocenedichloride, and so forth. Polymers made using metallocene catalyststypically have a narrow molecular weight range. For instance,metallocene-catalyzed polymers may have polydispersity numbers(M_(w)/M_(n)) of below 4, controlled short chain branching distribution,and controlled isotacticity.

The density of such α-olefin copolymers is a function of both the lengthand amount of the α-olefin. That is, the greater the length of theα-olefin and the greater the amount of α-olefin present, the lower thedensity of the copolymer. Although not necessarily required,substantially linear elastomers are particularly desirable in that thecontent of α-olefin short chain branching content is such that thecopolymer exhibits both plastic and elastomeric characteristics. Becausepolymerization with α-olefin comonomers decreases crystallinity anddensity, the resulting elastomer normally has a density lower than thatof polyethylene thermoplastic polymers (e.g., LLDPE), but approachingand/or overlapping that of other elastomers. For example, the density ofthe olefinic elastomer may be about 0.91 grams per cubic centimeter(g/cm³) or less, in some embodiments from about 0.85 to about 0.89g/cm³, and in some embodiments, from about 0.85 g/cm³ to about 0.88g/cm³.

Preferred ethylene elastomers for use in the present invention areethylene-based copolymer plastomers available under the EXACT™ fromExxonMobil Chemical Company of Houston, Tex. Other suitable polyethyleneplastomers are available under the designation ENGAGE™ and AFFINITY™from Dow Chemical Company of Midland, Mich. Still other suitableethylene polymers are available from The Dow Chemical Company under thedesignations DOWLEX™ (LLDPE) and ATTANE™ (ULDPE). Such ethylene polymersare described in U.S. Pat. No. 4,937,299 to Ewen et al.; U.S. Pat. No.5,218,071 to Tsutsui et al.; U.S. Pat. No. 5,272,236 to Lai et al.; andU.S. Pat. No. 5,278,272 to Lai, et al., which are incorporated herein intheir entirety by reference thereto for all purposes. Suitable propylenepolymers are commercially available under the designations VISTAMAXX™from ExxonMobil Chemical Co. of Houston, Tex.; FINA™ (e.g., 8573) fromAtofina Chemicals of Feluy, Belgium; TAFMER™ available from MitsuiPetrochemical Industries; and VERSIFY™ available from Dow Chemical Co.of Midland, Mich. Other examples of suitable propylene polymers aredescribed in U.S. Pat. No. 6,500,563 to Datta, et al.; U.S. Pat. No.5,539,056 to Yang, et al.; and U.S. Pat. No. 5,596,052 to Resconi, etal., which are incorporated herein in their entirety by referencethereto for all purposes.

The melt flow index (MI) of the olefinic elastomers may generally vary,but is typically in the range of about 0.1 grams per 10 minutes to about100 grams per 10 minutes, in some embodiments from about 0.5 grams per10 minutes to about 30 grams per 10 minutes, and in some embodiments,about 1 to about 10 grams per 10 minutes, determined at 190° C. The meltflow index is the weight of the polymer (in grams) that may be forcedthrough an extrusion rheometer orifice (0.0825-inch diameter) whensubjected to a force of 2.16 kilograms in 10 minutes at 190° C., and maybe determined in accordance with ASTM Test Method D1238-E.

Of course, other olefinic elastomers may also be employed in the presentinvention. In one embodiment, for example, the thermoplastic elastomermay be a styrene-olefin block copolymer, such asstyrene-(ethylene-butylene), styrene-(ethylene-propylene),styrene-(ethylene-butylene)-styrene,styrene-(ethylene-propylene)-styrene,styrene-(ethylene-butylene)-styrene-(ethylene-butylene),styrene-(ethylene-propylene)-styrene-(ethylene-propylene), andstyrene-ethylene-(ethylene-propylene)-styrene. Such polymers may beformed by selective hydrogenation of styrene-diene block copolymers,such as described in U.S. Pat. Nos. 4,663,220, 4,323,534, 4,834,738,5,093,422 and 5,304,599, which are hereby incorporated in their entiretyby reference thereto for all purposes. Particularly suitablethermoplastic elastomers are available from Kraton Polymers LLC ofHouston, Tex. under the trade name KRATON®. Other commercially availableblock copolymers include the S-EP-S elastomeric copolymers availablefrom Kuraray Company, Ltd. of Okayama, Japan, under the tradedesignation SEPTON®. Also suitable are polymers composed of an A-B-A-Btetrablock copolymer, such as discussed in U.S. Pat. No. 5,332,613 toTaylor, et al., which is incorporated herein in its entirety byreference thereto for all purposes. An example of such a tetrablockcopolymer is astyrene-poly(ethylene-propylene)-styrene-poly(ethylene-propylene)(“S-EP-S-EP”) block copolymer.

B. Water-Soluble Polymer

The film also includes one or more water-soluble polymers. Such polymersmay be formed from monomers such as vinyl pyrrolidone, hydroxyethylacrylate or methacrylate (e.g., 2-hydroxyethyl methacrylate),hydroxypropyl acrylate or methacrylate, acrylic or methacrylic acid,acrylic or methacrylic esters or vinyl pyridine, acrylamide, vinylacetate, vinyl alcohol (hydrolyzed from vinyl acetate), ethylene oxide,derivatives thereof, and so forth. Other examples of suitable monomersare described in U.S. Pat. Nos. 4,499,154 to James, et al., which isincorporated herein in its entirety by reference thereto for allpurposes. The resulting polymers may be homopolymers or interpolymers(e.g., copolymer, terpolymer, etc.), and may be nonionic, anionic,cationic, or amphoteric. In addition, the polymer may be of one type(i.e., homogeneous), or mixtures of different polymers may be used(i.e., heterogeneous). In one particular embodiment, the water-solublepolymer contains a repeating unit having a functional hydroxyl group,such as polyvinyl alcohol (“PVOH”), copolymers of polyvinyl alcohol(e.g., ethylene vinyl alcohol copolymers, methyl methacrylate vinylalcohol copolymers, etc.), etc. Vinyl alcohol polymers, for instance,have at least two or more vinyl alcohol units in the molecule and may bea homopolymer of vinyl alcohol, or a copolymer containing other monomerunits. Vinyl alcohol homopolymers may be obtained by hydrolysis of avinyl ester polymer, such as vinyl formate, vinyl acetate, vinylpropionate, etc. Vinyl alcohol copolymers may be obtained by hydrolysisof a copolymer of a vinyl ester with an olefin having 2 to 30 carbonatoms, such as ethylene, propylene, 1-butene, etc.; an unsaturatedcarboxylic acid having 3 to 30 carbon atoms, such as acrylic acid,methacrylic acid, crotonic acid, maleic acid, fumaric acid, etc., or anester, salt, anhydride or amide thereof; an unsaturated nitrile having 3to 30 carbon atoms, such as acrylonitrile, methacrylonitrile, etc.; avinyl ether having 3 to 30 carbon atoms, such as methyl vinyl ether,ethyl vinyl ether, etc.; and so forth.

The degree of hydrolysis may be selected to optimize solubility, etc.,of the polymer. For example, the degree of hydrolysis may be from about60 mole % to about 95 mole %, in some embodiments from about 80 mole %to about 90 mole %, and in some embodiments, from about 85 mole % toabout 89 mole %. Examples of suitable partially hydrolyzed polyvinylalcohol polymers are available under the designation CELVOL™ 203, 205,502, 504, 508, 513, 518, 523, 530, or 540 from Celanese Corp. Othersuitable partially hydrolyzed polyvinyl alcohol polymers are availableunder the designation ELVANOL™ 50-14, 50-26, 50-42, 51-03, 51-04, 51-05,51-08, and 52-22 from DuPont.

The water-soluble polymers employed in the present invention generallyhave a low molecular weight. For example, the water-soluble polymers mayhave a number average molecular weight (“M_(n)”) ranging from about1,000 to about 80,000 grams per mole, in some embodiments from about5,000 to about 60,000 grams per mole, and in some embodiments, fromabout 10,000 to about 40,000 grams per mole. Likewise, the water-solublepolymers may also have a weight average molecular weight (“M_(w)”)ranging from about 10,000 to about 150,000 grams per mole, in someembodiments from about 20,000 to about 100,000 grams per mole, and insome embodiments, from about 30,000 to about 75,000 grams per mole. Theratio of the weight average molecular weight to the number averagemolecular weight (“M_(w)/M_(n)”), i.e., the “polydispersity index”, isalso relatively low. For example, the polydispersity index typicallyranges from about 1.0 to about 4.0, in some embodiments from about 1.1to about 3.0, and in some embodiments, from about 1.2 to about 2.5. Thewater-soluble polymers may also have a solution viscosity of from about50 to about 800 milliPascal seconds (mPa·s), in some embodiments fromabout 100 to about 700 mPa·s, and in some embodiments, from about 200 toabout 600 mPa·s. The solution viscosity is measured as a 4 percentaqueous solution at 20° C. by the Hoeppler falling ball method inaccordance with ASTM-D 1343-56 Part 8, 1958, page 486.

A plasticizer is also employed in the present invention to help renderthe water-soluble polymer melt-processible. Suitable plasticizers mayinclude, for instance, polyhydric alcohol plasticizers, such as sugars(e.g., glucose, sucrose, fructose, raffinose, maltodextrose, galactose,xylose, maltose, lactose, mannose, and erythrose), sugar alcohols (e.g.,erythritol, xylitol, malitol, mannitol, and sorbitol), poiyols (e.g.,ethylene glycol, glycerol, propylene glycol, dipropylene glycol,butylene glycol, and hexane triol), etc. Also suitable are hydrogen bondforming organic compounds which do not have hydroxyl group, includingurea and urea derivatives; anhydrides of sugar alcohols such assorbitan; animal proteins such as gelatin; vegetable proteins such assunflower protein, soybean proteins, cotton seed proteins; and mixturesthereof. Other suitable plasticizers may include phthalate esters,dimethyl and diethylsuccinate and related esters, glycerol triacetate,glycerol mono and diacetates, glycerol mono, di, and tripropionates,butanoates, stearates, lactic acid esters, citric acid esters, adipicacid esters, stearic acid esters, oleic acid esters, and other acidesters. Aliphatic acids may also be used, such as copolymers of ethyleneand acrylic acid, polyethylene grafted with maleic acid,polybutadiene-co-acrylic acid, polybutadiene-co-maleic acid,polypropylene-co-acrylic acid, polypropylene-co-maleic acid, and otherhydrocarbon based acids. A low molecular weight plasticizer ispreferred, such as less than about 20,000 g/mol, preferably less thanabout 5,000 g/mol and more preferably less than about 1,000 g/mol.

Typically, the weight ratio of the water-soluble polymer to theplasticizer may be from about 1 to about 50, in some embodiments fromabout 2 to about 25, and in some embodiments, from about 3 to about 15.For example, a blend of plasticizer and water-soluble polymer(“plasticized water-soluble polymer”) may contain from about 1 wt. % toabout 40 wt. %, in some embodiments from about 2 wt. % to about 30 wt.%, and in some embodiments, from about 5 wt. % to about 25 wt. % of theplasticizer, and also from about 60 wt. % to about 99 wt. %, in someembodiments from about 70 wt. % to about 98 wt. %, and in someembodiments, from about 75 wt. % to about 95 wt. % of the water-solublepolymer.

Through selective control over the nature of the water-soluble polymer(e.g., molecular weight, viscosity, etc.), the nature of theplasticizer, and the relative amounts of the water-soluble polymer andplasticizer, the resulting plasticized water-soluble polymer may achievea melt viscosity that is similar to that of the olefinic elastomer,which further helps minimize phase separation during formation of thefilm. That is, the ratio of the melt viscosity of the olefinic elastomerto the plasticized water-soluble polymer is typically from about 0.6 toabout 2.5, in some embodiments from about 0.8 to about 2.2, and in someembodiments, from about 0.9 to about 2. For example, the plasticizedwater-soluble polymer may have an apparent melt viscosity of from about10 to about 400 Pascal seconds (Pa·s), in some embodiments from about 20to about 200 Pa·s, and in some embodiments, from about 30 to about 80Pa·s, as determined at a temperature of 195° C. and a shear rate of 1000sec⁻¹. Likewise, the apparent melt viscosity of the olefinic elastomermay range from about 20 to about 500 Pascal seconds (Pa·s), in someembodiments from about 30 to about 200 Pa·s, and in some embodiments,from about 40 to about 100 Pa·s, as determined at a temperature of 195°C. and a shear rate of 1000 sec⁻¹.

The relative amount of the water-soluble polymer and olefinic elastomeremployed in the film may also be selected to help further minimize phaseseparation. For example, the weight ratio of the water-soluble polymerto the olefinic elastomer is typically from about 0.01 to about 3.0, insome embodiments from about 0.1 to about 2.5, and in some embodiments,from about 1.0 to about 2.0. The olefinic elastomer may constitute fromabout 10 wt. % to about 70 wt. %, in some embodiments from about 15 wt.% to about 60 wt. %, and in some embodiments, from about 20 wt. % toabout 50 wt. % of the film. The water-soluble polymer may constitutefrom about 20 wt. % to about 90 wt. %, in some embodiments from about 30wt. % to about 80 wt. %, and in some embodiments, from about 40 wt. % toabout 70 wt. % of the film. Likewise, the plasticizer may constitutefrom about 1 wt. % to about 30 wt. %, in some embodiments from about 2wt. % to about 20 wt. %, and in some embodiments, from about 5 wt. % toabout 15 wt. % of the film.

C. Slip Additive

If desired, slip additives may also be employed in the present inventionto help reduce adhesion between the different polymer phases, therebyminimizing the formation of separate melt phases. Suitable slipadditives include, for instance, salts or amides of fatty acids saltderivatives of aromatic or aliphatic hydrocarbon oils, notably metalsalts of saturated or unsaturated fatty acids having a chain length of 7to 26 carbon atoms, preferably 10 to 22 carbon atoms. Examples ofsuitable fatty acids include the monocarboxylic acids lauric acid,stearic acid, succinic acid, stearyl lactic acid, lactic acid, phthalicacid, benzoic acid, hydroxystearic acid, ricinoleic acid, naphthenicacid, oleic acid, palmitic acid, erucic acid, etc. Suitable metalsinclude Li, Na, Mg, Ca, Sr, Ba, Zn, Cd, Al, Sn, Pb and so forth.Representative fatty acid salts include, for example, magnesiumstearate, calcium stearate, sodium stearate, zinc stearate, calciumoleate, zinc oleate, magnesium oleate, etc. Representative fatty acidamides having the formula, RC(O)NHR¹, where R is a saturated orunsaturated alkyl group having of from 7 to 26 carbon atoms, preferably10 to 22 carbon atoms, and R¹ is independently hydrogen or a saturatedor unsaturated alkyl group having from 7 to 26 carbon atoms, preferably10 to 22 carbon atoms. Exemplary compounds of this structure includepalmitamide, stearamide, arachidamide, behenamide, oleamide, erucamide,linoleamide, stearyl stearamide, palmityl palmitamide, stearylarachidamide, etc.

The slip additive may be blended with a carrier resin to form amasterbatch. Among other things, the carrier resin enhances thecompatibility of the additive with the other polymers used to form thefilm. Because the additive is more miscible with amorphous regions of apolymer than the crystalline regions, the carrier resin is generallyamorphous or semi-crystalline to optimize compatibility. Exemplaryamorphous polymers include polystyrene, polycarbonate, acrylic,acrylonitrile-butadiene-styrene (ABS), styrene-acrylonitrile, andpolysulfone. Exemplary semi-crystalline polymers include high and lowdensity polyethylene, polypropylene, polyoxymethylene, poly(vinylidinefluoride), poly(methyl pentene), poly(ethylene-chlorotrifluoroethylene),poly(vinyl fluoride), poly(ethylene oxide), poly(ethyleneterephthalate), poly(butylene terephthalate), nylon 6, nylon 66,poly(vinyl alcohol) and polybutene. Particularly suitable carrier resinsinclude polyolefins, such as ethylene-based polymers (e.g., DOWLEX™2517; Dow LLDPE DNDA-1082, Dow LLDPE DNDB-1077, Dow LLDPE 1081, and DowLLDPE DNDA 7147. In some instances, higher density polymers may beuseful, such as Dow HDPE DMDA-8980. Commercially available examples ofslip additive masterbatches include AMPACET™ 10090 (Ampacet NorthAmerica), which is believed to contain 5 wt. % of erucamide in lowdensity polyethylene (LDPE).

When employed, the carrier resin of the slip additive masterbatch mayconstitute from about 80 wt. % to about 99 wt. %, in some embodimentsfrom about 85 wt. % to about 98 wt. %, and in some embodiments, fromabout 90 wt. % to about 97 wt. % of the masterbatch. The slip additivemay likewise constitute from about 1 wt. % to about 20 wt. %, in someembodiments from about 2 wt. % to about 15 wt. %, and in someembodiments, from about 3 wt. % to about 10 wt. % of the masterbatch. Inturn, the masterbatch may also constitute from about 0.05 wt. % to about10 wt. %, in some embodiments from about 0.1 wt. % to about 5 wt. %, andin some embodiments, from about 0.5 wt. % to about 4 wt. % of the film.

D. Compatibilizer

A compatibilizer may also be employed in the film to further enhance thecompatibility between the polyolefin and water-soluble polymer. Whenemployed, such compatibilizers typically constitute from about 1 wt. %to about 20 wt. %, in some embodiments from about 2 wt. % to about 15wt. %, and in some embodiments, from about 4 wt. % to about 10 wt. % ofthe film. For example, the compatibilizer may be a functionalizedpolyolefin that possesses a polar component provided by one or morefunctional groups that is compatible with the water-soluble polymer anda non-polar component provided by an olefin that is compatible with theolefinic elastomer. The polar component may, for example, be provided byone or more functional groups and the non-polar component may beprovided by an olefin. The olefin component of the compatibilizer maygenerally be formed from any linear or branched α-olefin monomer,oligomer, or polymer (including copolymers) derived from an olefinmonomer. The α-olefin monomer typically has from 2 to 14 carbon atomsand preferably from 2 to 6 carbon atoms. Examples of suitable monomersinclude, but not limited to, ethylene, propylene, butene, pentene,hexene, 2-methyl-1-propene, 3-methyl-1-pentene, 4-methyl-1-pentene, and5-methyl-1-hexene. Examples of polyolefins include both homopolymers andcopolymers, i.e., polyethylene, ethylene copolymers such as EPDM,polypropylene, propylene copolymers, and polymethylpentene polymers. Anolefin copolymer can include a minor amount of non-olefinic monomers,such as styrene, vinyl acetate, diene, or acrylic and non-acrylicmonomer.

Functional groups may be incorporated into the polymer backbone using avariety of known techniques. For example, a monomer containing thefunctional group may be grafted onto a polyolefin backbone to form agraft copolymer. Such grafting techniques are well known in the art anddescribed, for instance, in U.S. Pat. No. 5,179,164, which isincorporated herein in its entirety by reference thereto for allpurposes. In other embodiments, the monomer containing the functionalgroups may be copolymerized with an olefin monomer to form a block orrandom copolymer. Regardless of the manner in which it is incorporated,the functional group of the compatibilizer may be any group thatprovides a polar segment to the molecule, such as a carboxyl group, acidanhydride group, acid amide group, imide group, carboxylate group, epoxygroup, amino group, isocyanate group, group having oxazoline ring,hydroxyl group, and so forth. Examples of compounds containing suchfunctional groups include aliphatic carboxylic acids; aromaticcarboxylic acids; esters; acid anhydrides and acid amides of theseacids; imides derived from these acids and/or acid anhydrides; aliphaticglycols or phenols; isocyanates, such as toluene diisocyanate andmethylenebis-(4-phenyl isocyanate); oxazolines, such as2-vinyl-2-oxazoline; epoxy compounds, such as epichlorohydrin andglycidyl methacrylate; aliphatic amines (e.g., monoamines, diamines,amines, or tetramines); aromatic amines, such as m-phenylenediamine; andso forth. Particularly suitable functional groups are maleic anhydride,maleic acid, fumaric acid, maleimide, maleic acid hydrazide, a reactionproduct of maleic anhydride and diamine, methylnadic anhydride,dichloromaleic anhydride, maleic acid amide and, natural fats and oilssuch as soybean oil, tung oil, caster oil, linseed oil, hempseed oil,cottonseed oil, sesame oil, rapeseed oil, peanut oil, camellia oil,olive oil, coconut oil and sardine oil; unsaturated carboxylic acid suchas acrylic acid, butenoic acid, crotonic acid, vinyl acetic acid,methacrylic acid, pentenoic acid, angelic acid, tiglic acid, 2-pentenoicacid, 3-pentenoic acid, α-ethylacrylic acid, β-methylcrotonic acid,4-pentenoic acid, 2-methyl-2-pentenoic acid, 3-methyl-2-pentenoic acid,oc-ethylcrotonic acid, 2,2-dimethyl-3-butenoic acid, 2-heptenoic acid,2-octenoic acid, 4-decenoic acid, 9-undecenoic acid, 10-undecenoic acid,4-dodecenoic acid, 5-dodecenoic acid, 4-tetradecenoic acid,9-tetradecenoic acid, 9-hexadecenoic acid, 2-octadecenoic acid,9-octadecenoic acid, eicosenoic acid, docosenoic acid, erucic acid,tetracocenoic acid, mycolipenic acid, 2,4-pentadienic acid,2,4-hexadienic acid, diallyl acetic acid, geranic acid, 2,4-decadienicacid, 2,4-dodecadienic acid, 9,12-hexadecadienic acid,9,12-octadecadienic acid, hexadecatrienic acid, linolic acid, linolenicacid, octadecatrienic acid, eicosadienic acid, eicosatrienic acid,eicosatetraenic acid, ricinoleic acid, eleosteric acid, oleic acid,eicosapentaenic acid, erucic acid, docosadienic acid, docosatrienicacid, docosatetraenic acid, docosapentaenic acid, tetracosenoic acid,hexacosenoic acid, hexacodienoic acid, octacosenoic acid, andtetraaconitic acid; ester, acid amide or anhydride of these unsaturatedcarboxylic acid above; etc.

Maleic anhydride modified polyolefins are particularly suitable for usein the present invention. Such modified polyolefins are typically formedby grafting maleic anhydride onto a polymeric backbone material. Suchmaleated polyolefins are available from E. I. du Pont de Nemours andCompany under the designation Fusabond®, such as the P Series(chemically modified polypropylene), E Series (chemically modifiedpolyethylene), C Series (chemically modified ethylene vinyl acetate), ASeries (chemically modified ethylene acrylate copolymers orterpolymers), or N Series (chemically modified ethylene-propylene,ethylene-propylene diene monomer (“EPDM”) or ethylene-octene).Alternatively, maleated polyolefins are also available from ChemturaCorp. under the designation Polybond® and Eastman Chemical Company underthe designation Eastman G series.

Regardless of the specific manner in which it is formed, a variety ofaspects of the compatibilizer may be selectively controlled to optimizeits ability to be employed in a film. For example, the weight percentageof polar groups in the compatibilizer may influence the ability to blendtogether the olefinic elastomer and water-soluble polymer. If the polargroup modification level is too high, for instance, film formation maybe restricted due to strong molecular interactions and physical networkformation by the polar groups. Conversely, if the polar groupmodification level is too low, compatibilization efficiency may bereduced. Thus, the polar functional groups (e.g., maleic anhydride)typically constitute from about 0.2 wt. % to about 10 wt. %, in someembodiments from about 0.5 wt. % to about 5 wt. %, and in someembodiments, from about 1 wt. % to about 3 wt. % of the compatibilizer.Likewise, the polyolefin component typically constitutes from about 90wt. % to about 99.8 wt. %, in some embodiments from about 95 wt. % toabout 99.5 wt. %, and in some embodiments, from about 97 wt. % to about99 wt. % of the compatibilizer. In addition, the melt flow rate of thecompatibilizer may also be controlled so that film formation is notadversely affected. For instance, the melt flow rate of thecompatibilizer may range from about 100 to about 600 grams per 10minutes, in some embodiments from about 200 to about 500 grams per 10minutes, and in some embodiments, from about 250 to about 450 grams per10 minutes, measured at a load of 2160 grams at a temperature of 190° C.in accordance with ASTM Test Method D1238-E.

E. Other Components

Other components may also be incorporated into the film as is known inthe art. In one embodiment, for example, the film may include a starch.Although starch is produced in many plants, typical sources includesseeds of cereal grains, such as corn, waxy corn, wheat, sorghum, rice,and waxy rice; tubers, such as potatoes; roots, such as tapioca (i.e.,cassava and manioc), sweet potato, and arrowroot; and the pith of thesago palm. Broadly speaking, native (unmodified) and/or modifiedstarches may be employed. Modified starches, for instance, may beemployed that have been chemically modified by typical processes knownin the art (e.g., esterification, etherification, oxidation, enzymatichydrolysis, etc.). Starch ethers and/or esters may be particularlydesirable, such as hydroxyalkyl starches, carboxymethyl starches, etc.The hydroxyalkyl group of hydroxylalkyl starches may contain, forinstance, 2 to 10 carbon atoms, in some embodiments from 2 to 6 carbonatoms, and in some embodiments, from 2 to 4 carbon atoms. Representativehydroxyalkyl starches such as hydroxyethyl starch, hydroxypropyl starch,hydroxybutyl starch, and derivatives thereof. Starch esters, forinstance, may be prepared using a wide variety of anhydrides (e.g.,acetic, propionic, butyric, and so forth), organic acids, acidchlorides, or other esterification reagents. The degree ofesterification may vary as desired, such as from 1 to 3 ester groups perglucosidic unit of the starch.

Further, the film may also contain one or more bioldegradablepolyesters. The term “biodegradable” generally refers to a material thatdegrades from the action of naturally occurring microorganisms, such asbacteria, fungi, and algae; environmental heat; moisture; or otherenvironmental factors, such as determined according to ASTM Test Method5338.92. Examples of suitable biodegradable polyesters include aliphaticpolyesters, such as polycaprolactone, polyesteramides, modifiedpolyethylene terephthalate, polylactic acid (PLA) and its copolymers,terpolymers based on polylactic acid, polyglycolic acid, polyalkylenecarbonates (such as polyethylene carbonate), polyhydroxyalkanoates(PHA), poly-3-hydroxybutyrate (PHB), poly-3-hydroxyvalerate (PHV),poly-3-hydroxybutyrate-co-4-hydroybutyrate,poly-3-hydroxybutyrate-co-3-hydroxyvalerate copolymers (PH BV),poly-3-hydroxybutyrate-co-3-hydroxyhexanoate,poly-3-hydroxybutyrate-co-3-hydroxyoctanoate,poly-3-hydroxybutyrate-co-3-hydroxydecanoate,poly-3-hydroxybutyrate-co-3-hydroxyoctadecanoate, and succinate-basedaliphatic polymers (e.g., polybutylene succinate, polybutylene succinateadipate, polyethylene succinate, etc.); aromatic polyesters and modifiedaromatic polyesters; and aliphatic-aromatic copolyesters. For example,the biodegradable polyester may be an aliphatic-aromatic copolyesterhaving the following structure:

wherein,

m is an integer from 2 to 10, in some embodiments from 2 to 4, and inone embodiment, 4;

n is an integer from 0 to 18, in some embodiments from 2 to 4, and inone embodiment, 4;

p is an integer from 2 to 10, in some embodiments from 2 to 4, and inone embodiment, 4;

x is an integer greater than 1; and

y is an integer greater than 1. One example of such a copolyester ispolybutylene adipate terephthalate, which is commercially availableunder the designation ECOFLEX® F BX 7011 from BASF Corp. Another exampleof a suitable copolyester containing an aromatic terephtalic acidmonomer constituent is available under the designation ENPOL™ 8060M fromIRE Chemicals (South Korea). Other suitable aliphatic-aromaticcopolyesters may be described in U.S. Pat. Nos. 5,292,783; 5,446,079;5,559,171; 5,580,911; 5,599,858; 5,817,721; 5,900,322; and 6,258,924,which are incorporated herein in their entirety by reference thereto forall purposes.

In addition to the components noted above, other additives may also beincorporated into the film of the present invention, such as dispersionaids, slip additives, melt stabilizers, processing stabilizers, heatstabilizers, light stabilizers, antioxidants, heat aging stabilizers,whitening agents, bonding agents, fillers, etc. Dispersion aids, forinstance, may also be employed to help create a uniform dispersion ofthe starch/polyvinyl alcohol/plasticizer mixture and retard or preventseparation into constituent phases. Likewise, the dispersion aids mayalso improve the water dispersibility of the film. When employed, thedispersion aid(s) typically constitute from about 0.01 wt. % to about 15wt. %, in some embodiments from about 0.1 wt. % to about 10 wt. %, andin some embodiments, from about 0.5 wt. % to about 5 wt. % of the film.Although any dispersion aid may generally be employed in the presentinvention, surfactants having a certain hydrophilic/lipophilic balance(“HLB”) may improve the long-term stability of the composition. The HLBindex is well known in the art and is a scale that measures the balancebetween the hydrophilic and lipophilic solution tendencies of acompound. The HLB scale ranges from 1 to approximately 50, with thelower numbers representing highly lipophilic tendencies and the highernumbers representing highly hydrophilic tendencies. In some embodimentsof the present invention, the HLB value of the surfactants is from about1 to about 20, in some embodiments from about 1 to about 15 and in someembodiments, from about 2 to about 10. If desired, two or moresurfactants may be employed that have HLB values either below or abovethe desired value, but together have an average HLB value within thedesired range.

One particularly suitable class of surfactants for use in the presentinvention are nonionic surfactants, which typically have a hydrophobicbase (e.g., long chain alkyl group or an alkylated aryl group) and ahydrophilic chain (e.g., chain contaiing ethoxy and/or propoxymoieties). For instance, some suitable nonionic surfactants that may beused include, but are not limited to, ethoxylated alkylphenols,ethoxylated and propoxylated fatty alcohols, polyethylene glycol ethersof methyl glucose, polyethylene glycol ethers of sorbitol, ethyleneoxide-propylene oxide block copolymers, ethoxylated esters of fatty(C₈-C₁₈) acids, condensation products of ethylene oxide with long chainamines or amides, condensation products of ethylene oxide with alcohols,fatty acid esters, monoglyceride or diglycerides of long chain alcohols,and mixtures thereof. In one particular embodiment, the nonionicsurfactant may be a fatty acid ester, such as a sucrose fatty acidester, glycerol fatty acid ester, propylene glycol fatty acid ester,sorbitan fatty acid ester, pentaerythritol fatty acid ester, sorbitolfatty acid ester, and so forth. The fatty acid used to form such estersmay be saturated or unsaturated, substituted or unsubstituted, and maycontain from 6 to 22 carbon atoms, in some embodiments from 8 to 18carbon atoms, and in some embodiments, from 12 to 14 carbon atoms. Inone particular embodiment, mono- and di-glycerides of fatty acids may beemployed in the present invention.

Fillers may also be employed in the present invention. Fillers areparticulates or other forms of material that may be added to the filmpolymer extrusion blend and that will not chemically interfere with theextruded film, but which may be uniformly dispersed throughout the film.Fillers may serve a variety of purposes, including enhancing filmopacity and/or breathability (i.e., vapor-permeable and substantiallyliquid-impermeable). For instance, filled films may be made breathableby stretching, which causes the polymer to break away from the fillerand create microporous passageways. Breathable microporous elastic filmsare described, for example, in U.S. Pat. Nos. 5,997,981; 6,015,764; and6,111,163 to McCormack, et al.; U.S. Pat. No. 5,932,497 to Morman, etal.; U.S. Pat. No. 6,461,457 to Taylor, et al., which are incorporatedherein in their entirety by reference thereto for all purposes. Further,hindered phenols are commonly used as an antioxidant in the productionof films. Some suitable hindered phenols include those available fromCiba Specialty Chemicals under the trade name “Irganox®”, such asIrganox® 1076, 1010, or E 201. Moreover, bonding agents may also beadded to the film to facilitate bonding of the film to additionalmaterials (e.g., nonwoven webs). Examples of such bonding agents includehydrogenated hydrocarbon resins. Other suitable bonding agents aredescribed in U.S. Pat. No. 4,789,699 to Kieffer et al. and U.S. Pat. No.5,695,868 to McCormack, which are incorporated herein in their entiretyby reference thereto for all purposes.

II. Film Construction

The film of the present invention may be mono- or multi-layered.Multilayer films may be prepared by co-extrusion of the layers,extrusion coating, or by any conventional layering process. Suchmultilayer films normally contain at least one base layer and at leastone skin layer, but may contain any number of layers desired. Forexample, the multilayer film may be formed from a base layer and one ormore skin layers, wherein the base layer is formed from a blend of thewater-soluble polymer and thermoplastic urethane. In most embodiments,the skin layer(s) are also formed from the blend as described above. Itshould be understood, however, that other polymers may also be employedin the skin layer(s).

Any known technique may be used to form a film from the compoundedmaterial, including blowing, casting, flat die extruding, etc. In oneparticular embodiment, the film may be formed by a blown process inwhich a gas (e.g., air) is used to expand a bubble of the extrudedpolymer blend through an annular die. The bubble is then collapsed andcollected in flat film form. Processes for producing blown films aredescribed, for instance, in U.S. Pat. No. 3,354,506 to Raley; U.S. Pat.No. 3,650,649 to Schippers; and U.S. Pat. No. 3,801,429 to Schrenk etal., as well as U.S. Patent Application Publication Nos. 2005/0245162 toMcCormack, et al. and 2003/0068951 to Boggs, et al., all of which areincorporated herein in their entirety by reference thereto for allpurposes. In yet another embodiment, however, the film is formed using acasting technique.

Referring to FIG. 1, for instance, one embodiment of a method forforming a cast film is shown. The raw materials (e.g., plasticizer,water-soluble polymer, olefinic elastomer, etc.) may be supplied to amelt blending device, either separately or as a blend. In oneembodiment, for example, the components are separately supplied to amelt blending device where they are dispersively blended in a mannersuch as described above. For example, an extruder may be employed thatincludes feeding and venting ports. In one embodiment, the olefinicelastomer may be fed to a feeding port of the twin-screw extruder andmelted. Thereafter, the plasticizer and water-soluble polymer may be fedinto the polymer melt. Regardless, the materials are blended under highshear/pressure and heat to ensure sufficient mixing. For example, meltblending may occur at a temperature of from about 75° C. to about 400°C., in some embodiments, from about 80° C. to about 300° C., and in someembodiments, from about 90° C. to about 250° C. Likewise, the apparentshear rate during melt blending may range from about 100 seconds⁻¹ toabout 10,000 seconds⁻¹, in some embodiments from about 500 seconds⁻¹ toabout 5000 seconds⁻¹, and in some embodiments, from about 800 seconds⁻¹to about 1200 seconds⁻¹. The apparent shear rate is equal to 4Q/πR³,where Q is the volumetric flow rate (“m³/s”) of the polymer melt and Ris the radius (“m”) of the capillary (e.g., extruder die) through whichthe melted polymer flows.

Thereafter, the extruded material may be immediately chilled and cutinto pellet form. In the particular embodiment of FIG. 1, the compoundedmaterial (not shown) is then supplied to an extrusion apparatus 80 andcast onto a casting roll 90 to form a single-layered precursor film 10a. If a multilayered film is to be produced, the multiple layers areco-extruded together onto the casting roll 90. The casting roll 90 mayoptionally be provided with embossing elements to impart a pattern tothe film. Typically, the casting roll 90 is kept at temperaturesufficient to solidify and quench the sheet 10 a as it is formed, suchas from about 20 to 60° C. If desired, a vacuum box may be positionedadjacent to the casting roll 90 to help keep the precursor film 10 aclose to the surface of the roll 90. Additionally, air knives orelectrostatic pinners may help force the precursor film 10 a against thesurface of the casting roll 90 as it moves around a spinning roll. Anair knife is a device known in the art that focuses a stream of air at avery high flow rate to pin the edges of the film.

Once cast, the film 10 a may then be optionally oriented in one or moredirections to further improve film uniformity and reduce thickness.Orientation may also form micropores in a film containing a filler, thusproviding breathability to the film. For example, the film may beimmediately reheated to a temperature below the melting point of one ormore polymers in the film, but high enough to enable the composition tobe drawn or stretched. In the case of sequential orientation, the“softened” film is drawn by rolls rotating at different speeds ofrotation such that the sheet is stretched to the desired draw ratio inthe longitudinal direction (machine direction). This “uniaxially”oriented film may then be laminated to a fibrous web. In addition, theuniaxially oriented film may also be oriented in the cross-machinedirection to form a “biaxially oriented” film. For example, the film maybe clamped at its lateral edges by chain clips and conveyed into atenter oven. In the tenter oven, the film may be reheated and drawn inthe cross-machine direction to the desired draw ratio by chain clipsdiverged in their forward travel.

Referring again to FIG. 1, for instance, one method for forming auniaxially oriented film is shown. As illustrated, the precursor film 10a is directed to a film-orientation unit 100 or machine directionorienter (“MDO”), such as commercially available from Marshall andWillams, Co. of Providence, Rhode Island. The MDO has a plurality ofstretching rolls (such as from 5 to 8) which progressively stretch andthin the film in the machine direction, which is the direction of travelof the film through the process as shown in FIG. 1. While the MDO 100 isillustrated with eight rolls, it should be understood that the number ofrolls may be higher or lower, depending on the level of stretch that isdesired and the degrees of stretching between each roll. The film may bestretched in either single or multiple discrete stretching operations.It should be noted that some of the rolls in an MDO apparatus may not beoperating at progressively higher speeds. If desired, some of the rollsof the MDO 100 may act as preheat rolls. If present, these first fewrolls heat the film 10 a above room temperature (e.g., to 125° F.). Theprogressively faster speeds of adjacent rolls in the MDO act to stretchthe film 10 a. The rate at which the stretch rolls rotate determines theamount of stretch in the film and final film weight.

The resulting film 10 b may then be wound and stored on a take-up roll60. While not shown here, various additional potential processing and/orfinishing steps known in the art, such as slitting, treating,aperturing, printing graphics, or lamination of the film with otherlayers (e.g., nonwoven web materials), may be performed withoutdeparting from the spirit and scope of the invention.

The thickness of the resulting water-sensitive elastic film maygenerally vary depending upon the desired use. Nevertheless, the filmthickness is typically minimized to reduce the time needed for the filmto disperse in water. Thus, in most embodiments of the presentinvention, the water-sensitive elastic film has a thickness of about 50micrometers or less, in some embodiments from about 1 to about 100micrometers, in some embodiments from about 5 to about 75 micrometers,and in some embodiments, from about 10 to about 60 micrometers.

Despite having such a small thickness and good sensitivity in water, thefilm of the present invention is nevertheless able to retain good drymechanical properties during use. One parameter that is indicative ofthe relative dry strength of the film is the ultimate tensile strength,which is equal to the peak stress obtained in a stress-strain curve.Desirably, the film of the present invention exhibits an ultimatetensile strength in the machine direction (“MD”) of from about 10 toabout 80 Megapascals (MPa), in some embodiments from about 15 to about60 MPa, and in some embodiments, from about 20 to about 50 MPa, and anultimate tensile strength in the cross-machine direction (“CD”) of fromabout 2 to about 40 Megapascals (MPa), in some embodiments from about 4to about 40 MPa, and in some embodiments, from about 5 to about 30 MPa.Although possessing good strength, it is also desirable that the film isnot too stiff. One parameter that is indicative of the relativestiffness of the film (when dry) is Young's modulus of elasticity, whichis equal to the ratio of the tensile stress to the tensile strain and isdetermined from the slope of a stress-strain curve. For example, thefilm typically exhibits a Young's modulus in the machine direction(“MD”) of from about 20 to about 800 Megapascals (“MPa”), in someembodiments from about 50 to about 500 MPa, and in some embodiments,from about 100 to about 400 MPa, and a Young's modulus in thecross-machine direction (“CD”) of from about 20 to about 800 Megapascals(“MPa”), in some embodiments from about 50 to about 500 MPa, and in someembodiments, from about 100 to about 400 MPa.

The film is also generally extensible in that it possesses an elongationin the machine and/or cross-machine direction of about 50% or more, insome embodiments about 100% or more, in some embodiments about 200% ormore, and in some embodiments, about 300% or more. Besides beingextensible, the film is also generally elastic in that is capable ofrecovering at least about 50% of its stretched length upon release ofthe stretching force. The elasticity of the film may be characterized byits “percent set”, which is typically about 30% or less, in someembodiments about 15% or less, in some embodiments about 10% or less,and in some embodiments, from about 0.001% to about 5%.

The water-sensitive elastic film of the present invention may be used ina wide variety of applications. For example, as indicated above, thefilm may be used in an absorbent article. An “absorbent article”generally refers to any article capable of absorbing water or otherfluids. Examples of some absorbent articles include, but are not limitedto, personal care absorbent articles, such as diapers, training pants,absorbent underpants, incontinence articles, feminine hygiene products(e.g., sanitary napkins, pantiliners, etc.), swim wear, baby wipes, andso forth; medical absorbent articles, such as garments, fenestrationmaterials, underpads, bedpads, bandages, absorbent drapes, and medicalwipes; food service wipers; clothing articles; and so forth. Severalexamples of such absorbent articles are described in U.S. Pat. No.5,649,916 to DiPalma, et al.; U.S. Pat. No. 6,110,158 to Kielipikowski;U.S. Pat. No. 6,663,611 to Blaney, et al., which are incorporated hereinin their entirety by reference thereto for all purposes. Still othersuitable articles are described in U.S. Patent Application PublicationNo. 2004/0060112 A1 to Fell et al., as well as U.S. Pat. No. 4,886,512to Damico et al.; U.S. Pat. No. 5,558,659 to Sherrod et al.; U.S. Pat.No. 6,888,044 to Fell et al.; and U.S. Pat. No. 6,511,465 to Freiburgeret al., all of which are incorporated herein in their entirety byreference thereto for all purposes. Materials and processes suitable forforming such absorbent articles are well known to those skilled in theart.

As is well known in the art, the absorbent article may be provided withadhesives (e.g., pressure-sensitive adhesives) that help removablysecure the article to the crotch portion of an undergarment and/or wrapup the article for disposal. Suitable pressure-sensitive adhesives, forinstance, may include acrylic adhesives, natural rubber adhesives,tackified block copolymer adhesives, polyvinyl acetate adhesives,ethylene vinyl acetate adhesives, silicone adhesives, polyurethaneadhesives, thermosettable pressure-sensitive adhesives, such as epoxyacrylate or epoxy polyester pressure-sensitive adhesives, etc. Suchpressure-sensitive adhesives are known in the art and are described inthe Handbook of Pressure Sensitive Adhesive Technology, Satas (Donatas),1989, 2^(nd) edition, Van Nostrand Reinhold. The pressure sensitiveadhesives may also include additives such as cross-linking agents,fillers, gases, blowing agents, glass or polymeric microspheres, silica,calcium carbonate fibers, surfactants, and so forth. The additives areincluded in amounts sufficient to affect the desired properties.

The location of the adhesive on the absorbent article is not criticaland may vary widely depending on the intended use of the article. Forexample, certain feminine hygiene products (e.g., sanitary napkins) mayhave wings or flaps that extend laterally from a central absorbent coreand are intended to be folded around the edges of the wearer's pantiesin the crotch region. The flaps may be provided with an adhesive (e.g.,pressure-sensitive adhesive) for affixing the flaps to the underside ofthe wearer's panties.

Regardless of the particular location of the adhesive, however, arelease liner may be employed to cover the adhesive, thereby protectingit from dirt, drying out, and premature sticking prior to use. Therelease liner may contain a release coating that enhances the ability ofthe liner to be peeled from an adhesive. The release coating contains arelease agent, such as a hydrophobic polymer. Exemplary hydrophobicpolymers include, for instance, silicones (e.g., polysiloxanes, epoxysilicones, etc.), perfluoroethers, fluorocarbons, polyurethanes, and soforth. Examples of such release agents are described, for instance, inU.S. Pat. No. 6,530,910 to Pomplun, et al.; U.S. Pat. No. 5,985,396 toKerins, et al.; and U.S. Pat. No. 5,981,012 to Pomplun, et al., whichare incorporated herein in their entirety by reference thereto for allpurposes. One particularly suitable release agent is an amorphouspolyolefin having a melt viscosity of about 400 to about 10,000 cps at190° C., such as made by the U.S. Rexene Company under the tradenameREXTAC® (e.g., RT2315, RT2535 and RT2330). The release coating may alsocontain a detackifier, such as a low molecular weight, highly branchedpolyolefin. A particularly suitable low molecular weight, highlybranched polyolefin is VYBAR® 253, which is made by the PetroliteCorporation. Other additives may also be employed in the releasecoating, such as compatibilizers, processing aids, plasticizers,tackifiers, slip agents, and antimicrobial agents, and so forth. Therelease coating may be applied to one or both surfaces of the liner, andmay cover all or only a portion of a surface. Any suitable technique maybe employed to apply the release coating, such as solvent-based coating,hot melt coating, solventless coating, etc. Solvent-based coatings aretypically applied to the release liner by processes such as rollcoating, knife coating, curtain coating, gravure coating, wound rodcoating, and so forth. The solvent (e.g., water) is then removed bydrying in an oven, and the coating is optionally cured in the oven.Solventless coatings may include solid compositions, such as siliconesor epoxy silicones, which are coated onto the liner and then cured byexposure to ultraviolet light. Optional steps include priming the linerbefore coating or surface modification of the liner, such as with coronatreatment. Hot melt coatings, such as polyethylenes or perfluoroethers,may be heated and then applied through a die or with a heated knife. Hotmelt coatings may be applied by co-extruding the release agent with therelease liner in blown film or sheet extruder for ease of coating andfor process efficiency.

To facilitate its ability to be easily disposed, the release liner maybe formed from a water-sensitive film in accordance with the presentinvention. In this regard, one particular embodiment of a sanitarynapkin that may employ the water-sensitive film will now be described inmore detail. For purposes of illustration only, an absorbent article 20is shown in FIG. 2 as a sanitary napkin for feminine hygiene. In theillustrated embodiment, the absorbent article 20 includes a main bodyportion 22 containing a topsheet 40, an outer cover or backsheet 42, anabsorbent core 44 positioned between the backsheet 42 and the topsheet40, and a pair of flaps 24 extending from each longitudinal side 22 a ofthe main body portion 22. The topsheet 40 defines a bodyfacing surfaceof the absorbent article 20. The absorbent core 44 is positioned inwardfrom the outer periphery of the absorbent article 20 and includes abody-facing side positioned adjacent the topsheet 40 and agarment-facing surface positioned adjacent the backsheet 42.

The topsheet 40 is generally designed to contact the body of the userand is liquid-permeable. The topsheet 40 may surround the absorbent core44 so that it completely encases the absorbent article 20.Alternatively, the topsheet 40 and the backsheet 42 may extend beyondthe absorbent core 44 and be peripherally joined together, eitherentirely or partially, using known techniques. Typically, the topsheet40 and the backsheet 42 are joined by adhesive bonding, ultrasonicbonding, or any other suitable joining method known in the art. Thetopsheet 40 is sanitary, clean in appearance, and somewhat opaque tohide bodily discharges collected in and absorbed by the absorbent core44. The topsheet 40 further exhibits good strike-through and rewetcharacteristics permitting bodily discharges to rapidly penetratethrough the topsheet 40 to the absorbent core 44, but not allow the bodyfluid to flow back through the topsheet 40 to the skin of the wearer.For example, some suitable materials that may be used for the topsheet40 include nonwoven materials, perforated thermoplastic films, orcombinations thereof. A nonwoven fabric made from polyester,polyethylene, polypropylene, bicomponent, nylon, rayon, or like fibersmay be utilized. For instance, a white uniform spunbond material isparticularly desirable because the color exhibits good maskingproperties to hide menses that has passed through it. U.S. Pat. No.4,801,494 to Datta, et al. and U.S. Pat. No. 4,908,026 to Sukiennik. etal. teach various other cover materials that may be used in the presentinvention.

The topsheet 40 may also contain a plurality of apertures (not shown)formed therethrough to permit body fluid to pass more readily into theabsorbent core 44. The apertures may be randomly or uniformly arrangedthroughout the topsheet 40, or they may be located only in the narrowlongitudinal band or strip arranged along the longitudinal axis X-X ofthe absorbent article 20. The apertures permit rapid penetration of bodyfluid down into the absorbent core 44. The size, shape, diameter andnumber of apertures may be varied to suit one's particular needs.

As stated above, the absorbent article also includes a backsheet 42. Thebacksheet 42 is generally liquid-impermeable and designed to face theinner surface, i.e., the crotch portion of an undergarment (not shown).The backsheet 42 may permit a passage of air or vapor out of theabsorbent article 20, while still blocking the passage of liquids. Anyliquid-impermeable material may generally be utilized to form thebacksheet 42. For example, one suitable material that may be utilized isa microembossed polymeric film, such as polyethylene or polypropylene.In particular embodiments, a polyethylene film is utilized that has athickness in the range of about 0.2 mils to about 5.0 mils, andparticularly between about 0.5 to about 3.0 mils.

The absorbent article 20 also contains an absorbent core 44 positionedbetween the topsheet 40 and the backsheet 42. The absorbent core 44 maybe formed from a single absorbent member or a composite containingseparate and distinct absorbent members. It should be understood,however, that any number of absorbent members may be utilized in thepresent invention. For example, in one embodiment, the absorbent core 44may contain an intake member (not shown) positioned between the topsheet40 and a transfer delay member (not shown). The intake member may bemade of a material that is capable of rapidly transferring, in thez-direction, body fluid that is delivered to the topsheet 40. The intakemember may generally have any shape and/or size desired. In oneembodiment, the intake member has a rectangular shape, with a lengthequal to or less than the overall length of the absorbent article 20,and a width less than the width of the absorbent article 20. Forexample, a length of between about 150 mm to about 300 mm and a width ofbetween about 10 mm to about 60 mm may be utilized.

Any of a variety of different materials may be used for the intakemember to accomplish the above-mentioned functions. The material may besynthetic, cellulosic, or a combination of synthetic and cellulosicmaterials. For example, airlaid cellulosic tissues may be suitable foruse in the intake member. The airlaid cellulosic tissue may have a basisweight ranging from about 10 grams per square meter (gsm) to about 300gsm, and in some embodiments, between about 100 gsm to about 250 gsm. Inone embodiment, the airlaid cellulosic tissue has a basis weight ofabout 200 gsm. The airlaid tissue may be formed from hardwood and/orsoftwood fibers. The airlaid tissue has a fine pore structure andprovides an excellent wicking capacity, especially for menses.

If desired, a transfer delay member (not shown) may be positionedvertically below the intake member. The transfer delay member maycontain a material that is less hydrophilic than the other absorbentmembers, and may generally be characterized as being substantiallyhydrophobic. For example, the transfer delay member may be a nonwovenfibrous web composed of a relatively hydrophobic material, such aspolypropylene, polyethylene, polyester or the like, and also may becomposed of a blend of such materials. One example of a materialsuitable for the transfer delay member is a spunbond web composed ofpolypropylene, multi-lobal fibers. Further examples of suitable transferdelay member materials include spunbond webs composed of polypropylenefibers, which may be round, tri-lobal or poly-lobal in cross-sectionalshape and which may be hollow or solid in structure. Typically the websare bonded, such as by thermal bonding, over about 3% to about 30% ofthe web area. Other examples of suitable materials that may be used forthe transfer delay member are described in U.S. Pat. No. 4,798,603 toMeyer, et al. and U.S. Pat. No. 5,248,309 to Serbiak, et al., which areincorporated herein in their entirety by reference thereto for allpurposes. To adjust the performance of the invention, the transfer delaymember may also be treated with a selected amount of surfactant toincrease its initial wettability.

The transfer delay member may generally have any size, such as a lengthof about 150 mm to about 300 mm. Typically, the length of the transferdelay member is approximately equal to the length of the absorbentarticle 20. The transfer delay member may also be equal in width to theintake member, but is typically wider. For example, the width of thetransfer delay member may be from between about 50 mm to about 75 mm,and particularly about 48 mm. The transfer delay member typically has abasis weight less than that of the other absorbent members. For example,the basis weight of the transfer delay member is typically less thanabout 150 grams per square meter (gsm), and in some embodiments, betweenabout 10 gsm to about 100 gsm. In one particular embodiment, thetransfer delay member is formed from a spunbonded web having a basisweight of about 30 gsm.

Besides the above-mentioned members, the absorbent core 44 may alsoinclude a composite absorbent member (not shown), such as a coformmaterial. In this instance, fluids may be wicked from the transfer delaymember into the composite absorbent member. The composite absorbentmember may be formed separately from the intake member and/or transferdelay member, or may be formed simultaneously therewith. In oneembodiment, for example, the composite absorbent member may be formed onthe transfer delay member or intake member, which acts a carrier duringthe coform process described above.

Regardless of its particular construction, the absorbent article 20typically contains an adhesive for securing to an undergarment. Anadhesive may be provided at any location of the absorbent article 20,such as on the lower surface of the backsheet 42. In this particularembodiment, the backsheet 42 carries a longitudinally central strip ofgarment adhesive 54 covered before use by a peelable release liner 58,which may be formed in accordance with the present invention. Each ofthe flaps 24 may also contain an adhesive 56 positioned adjacent to thedistal edge 34 of the flap 24. A peelable release liner 57, which mayalso be formed in accordance with the present invention, may cover theadhesive 56 before use. Thus, when a user of the sanitary absorbentarticle 20 wishes to expose the adhesives 54 and 56 and secure theabsorbent article 20 to the underside of an undergarment, the usersimply peels away the liners 57 and 58 and disposed them in awater-based disposal system (e.g., in a toilet).

Although various configurations of a release liner have been describedabove, it should be understood that other release liner configurationsare also included within the scope of the present invention. Further,the present invention is by no means limited to release liners and thewater-sensitive elastic film may be incorporated into a variety ofdifferent components of an absorbent article. For example, referringagain to FIG. 2, the backsheet 42 of the napkin 20 may include thewater-sensitive film of the present invention. In such embodiments, thefilm may be used alone to form the backsheet 42 or laminated to one ormore additional materials, such as a nonwoven web. The water-sensitiveelastic film of the present invention may also be used in applicationsother than absorbent articles. For example, the film may be employed asan individual wrap, packaging pouch, or bag for the disposal of avariety of articles, such as food products, absorbent articles, etc.Various suitable pouch, wrap, or bag configurations for absorbentarticles are disclosed, for instance, in U.S. Pat. No. 6,716,203 toSorebo, et al. and U.S. Pat. No. 6,380,445 to Moder, et al., as well asU.S. Patent Application Publication No. 2003/0116462 to Sorebo, et al.,all of which are incorporated herein in their entirety by referencethereto for all purposes.

The present invention may be better understood with reference to thefollowing examples.

Test Methods

Apparent Melt Viscosity:

The rheological properties of polymer samples were determined using aGottfert Rheograph 2003 capillary rheometer with WinRHEO version 2.31analysis software. The setup included a 2000-bar pressure transducer anda 30/1:0/180 roundhole capillary die. Sample loading was done byalternating between sample addition and packing with a ramrod. A2-minute melt time preceded each test to allow the polymer to completelymelt at a test temperature (150° C. or 160° C.). The capillary rheometerdetermined the apparent melt viscosity (Pa·s) at various shear rates,such as 100, 200, 500, 1000, 2000, and 4000 s⁻¹. The resultant rheologycurve of apparent shear rate versus apparent melt viscosity gave anindication of how the polymer would run at that temperature in anextrusion process.

Tensile Properties:

The strip tensile strength values were determined in substantialaccordance with ASTM Standard D-5034. A constant-rate-of-extension typeof tensile tester was employed. The tensile testing system was a Sintech1/D tensile tester, which is available from Sintech Corp. of Cary, N.C.The tensile tester was equipped with TESTWORKS 4.08B software from MTSCorporation to support the testing. An appropriate load cell wasselected so that the tested value fell within the range of 10-90% of thefull scale load. The film samples were initially cut into dog-boneshapes with a center width of 3.0 mm before testing. The samples wereheld between grips having a front and back face measuring 25.4millimeters×76 millimeters. The grip faces were rubberized, and thelonger dimension of the grip was perpendicular to the direction of pull.The grip pressure was pneumatically maintained at a pressure of 40pounds per square inch. The tensile test was run using a gauge length of18.0 millimeters and a break sensitivity of 40%. Five samples weretested by applying the test load along the machine-direction and fivesamples were tested by applying the test load along the cross direction.During the test, samples were stretched at a crosshead speed of abut 127millimeters per minute until breakage occurred. The modulus, peakstress, and elongation were measured in the machine direction (“MD”) andcross-machine directions (“CD”).

Water Disintegration Test:

The rate of film disintegration in tap water was tested using a “sloshbox”, which has a physical dimension of a 14″×18″×12″ high plastic boxon a hinged platform. One end of the platform is attached to thereciprocating cam. The typical amplitude is ±2″ (4″ range), withsloshing occurring at 0.5˜1.5 sloshes per second. The preferred actionis 0.9˜1.3 sloshes per second. During a test, the slosh box rocks up anddown with the water inside, “sloshing” back and forth. This actionproduces a wave front and intermittent motion on a sample susceptible todispersing in water. To quantify a measurement of sample filmdisintegration in water, without image analysis, simply timing issufficient. Three liters of tap water were added into the slosh box andresulted in ˜5.5″ water depth in the box. A frequency of 3.5 wasselected for the testing. Each film sample was cut into 1″×3″ size.Three pieces were dropped into the slosh box. The time to disintegratethe sample under the defined conditions was recorded twice for eachsample. The average of the time to the sample disintegration is thenreported. Generally, films reach an acceptable dispersion point when nopiece is larger than 25 mm² in size within 6 hours of agitation.

Cycle Testing

The materials were tested using a cyclical testing procedure todetermine percent set. In particular, 1-cycle testing was utilized to100% defined elongation. The testing was done on a Sintech Corp.constant rate of extension tester 1/D equipped with TESTWORKS 4.08Bsoftware from MTS Corporation to support the testing. The test wasconducted under ambient conditions. For this test, the sample size was 1inches (2.54 centimeters) in the cross-machine direction by 3 inches(7.6 centimeter) in the machine direction. The grip size was 3 inches(7.6 centimeters) in width and the grip separation was 4 inches. Thesamples were loaded such that the machine direction of the sample was inthe vertical direction. A preload of approximately 20 to 30 grams wasset. The test pulled the sample to 100% elongation at a speed of 20inches (50.8 centimeters) per minute, held the sample in an elongatedstate for 30 seconds, and then returned the sample to zero elongation ata speed of 20 inches (50.8 centimeters) per minute. Thereafter, the filmlength was immediately measured and again measured in 10, 20, and 30minutes. The percent that did not recover (“percent set”) was determinedby subtracting the length of the film 30 minutes after cycle testingfrom the original length of the film, and then dividing this number bythe original length of the film.

EXAMPLE 1

A starch-based blend, which was a water-soluble polymer resin, wasformed from 16 wt. % ELVANOL™ 51-05 (polyvinyl alcohol, produced byDuPont, Wilmington, Del.), 44 wt. % GLUCOSOL™ 800 (Chemstar,Minneapolis, Minn.), 20% glycerol (Cognis Corporation, Cincinnati, Ohio)and 20 wt. % ECOFLEX™ F BX 7011 (BASF, Mount Olive, N.J.). Thesecomponents were fed into a co-rotating twin screw extruder (ZSK-30,Werner and Pfleiderer Corporation, Ramsey, N.J.). The extruder diameterwas 30 mm and the length of the screws was up to 1328 mm. The extruderhas 14 barrels, numbered consecutively 1 to 14 from the feed hopper tothe die. The temperature profile of zones 1 to 14 of the extruder was110° C., 130° C., 190° C., 190° C., 190° C., 180° C., and 170° C.,respectively. The screw speed was set at 150 rpm to achieve a torque ofbetween 45˜50%, P_(melt) of 130˜200 psi, and an output of about 18 to 20lb/hr. The thermoplastic blend was then dry blended with VISTAMAXX™1120, which is a metallocene-catalyzed ethylene/propylene copolymer fromExxonMobil, using HAAKE Rheomex 252 single screw extruder for filmcasting. The screw speed was set at 40 to 50 rpm and the temperatureprofile of the extruder from zone 1 to 5 was 190° C., 200° C., 200° C.,198° C., and 175° C., respectively. The melt temperature was 195° C. Theresulting film had a thickness of about 0.002 inches (˜50.8micrometers). The water disintegration test indicated that the film wasnot generally water sensitive.

EXAMPLE 2

Another water-soluble polymer resin was formed from 72 wt. % CELVOL™523S (polyvinyl alcohol, Celanese), 10 wt. % talc (MP 30-36, BarrettsMinerals, Dillon, Mont.) and 18 wt. % glycerin (Cognis Corporation,Cincinnati, Ohio). The blend was then dry blended with 15 wt. %VISTAMAXX™ 6102, which is a metallocene-catalyzed ethylene/propylenecopolymer from ExxonMobil and 5 wt. % FUSABOND™ (functionalizedpolyethylene-based compatibilizer from DuPont). Film casting was notsuccessful in this particular instance.

EXAMPLE 3

A water-soluble polymer resin was formed from 66 wt. % CELVOL™ 523S(polyvinyl alcohol, Celanese), 20 wt. % talc (MP 30-36, BarrettsMinerals, Dillon, Mont.) and 14 wt. % glycerin (Cognis Corporation,Cincinnati, Ohio). The blend was then dry blended with 15 wt. %VISTAMAXX™ 1120, which is a metallocene-catalyzed ethylene/propylenecopolymer from ExxonMobil and 5 wt. % FUSABOND™ (functionalizedpolyethylene-based compatibilizer from DuPont). These components werefed into a co-rotating twin screw extruder (ZSK-30, Werner andPfleiderer Corporation, Ramsey, N.J.). The extruder diameter was 30 mmand the length of the screws was up to 1328 mm. The extruder has 14barrels, numbered consecutively 1 to 14 from the feed hopper to the die.The temperature profile of zones 1 to 14 of the extruder was 110° C.,130° C., 190° C., 190° C., 190° C., 180° C., and 170° C., respectively.The screw speed was set at 150 rpm to achieve a torque of between45-50%, P_(melt) of 130-200 psi, and an output of about 18 to 20 lb/hr.The resulting film was water soluble and had a thickness of about 0.002inches. The strength of the film in the MD and CD directions, however,was not isotropic.

EXAMPLE 4

A blend was formed 55 wt. % of a water-soluble polymer, 25 wt. % of anelastomer, and 20 wt. % of a plasticizer. The water-soluble polymer wasCELVOL™ 523S (polyvinyl alcohol, Celanese). The elastomer was KRATON™G1657, a styrene-ethylene/butylene-styrene block copolymer from KratonPolymers of Houston, Tex. The plasticizer was glycerin (CognisCorporation, Cincinnati, Ohio). These components were fed into aco-rotating twin screw extruder (ZSK-30, Werner and PfleidererCorporation, Ramsey, N.J.). The extruder diameter was 30 mm and thelength of the screws was up to 1328 mm. The extruder has 14 barrels,numbered consecutively 1 to 14 from the feed hopper to the die. Thetemperature profile of zones 1 to 14 of the extruder was 110° C., 130°C., 190° C., 190° C., 190° C., 180° C., and 170° C., respectively. Thescrew speed was set at 150 rpm to achieve a torque of between 45-50%,P_(melt) of 130-200 psi, and an output of about 18 to 20 lb/hr. Thestrand obtained from compounding was rough, indicating that thematerials were not compatible. No film was formed.

EXAMPLE 5

A plasticized PVOH was formed from ELVANOL™ 51-05 (DuPont), which wasobtained by feeding 85 wt. % PVOH powder into a co-rotating twin screwextruder (ZSK-30, Werner and Pfleiderer Corporation, Ramsey, N.J.).Glycerin (Cognis Corporation, Cincinnati, Ohio) was used as aplasticizer that was fed at 15 wt % into the zone 1 by an Eldex pump.The extruder diameter was 30 mm and the length of the screws was up to1328 mm. The extruder has 14 barrels, numbered consecutively 1 to 14from the feed hopper to the die. The temperature profile of zones 1 to14 of the extruder was 95° C., 145° C., 185° C., 185° C., 175° C., 160and 155° C., respectively. The screw speed was set at 150 rpm to achievea torque of between 50˜55%, P_(melt) of 180˜190 psi, and an output ofabout 19 lb/hr.

EXAMPLES 6-7

Two (2) films were formed by a way of dry blending of the plasticizedpolyvinyl alcohol from Example 5 and VISTAMAXX™ 1120 on HAAKE Rheomex252 Single Screw Extruder. The ratio of the plasticized PVOH toVISTAMAXX™ 1120 was 60/40 for Example 6 and 70/30 for Example 7. Thescrew speed was set at 40 to 50 rpm and the temperature profile of theextruder from zone 1 to 5 was 190° C., 200° C., 200° C., 198° C., and175° C., respectively. The melt temperature was 195° C. The resultingfilm had a thickness of about 0.002 inches (˜50.8 micrometers).

EXAMPLE 8

A film was formed as described in Example 6, except that it contained 1wt. % of a slip additive (Clarity Slip PE MB produced by AmpacetCorporation, Tarrytown, N.Y.).

EXAMPLES 9-10

Two (2) films were formed as described in Examples 6-7, except that used1 wt. % of Clarity Slip PE MB and 5 wt. % FUSABOND™ MC 190D. Example 9kept the same ratio of the plasticized polyvinyl alcohol to VISTAMAXX™1120 shown in Example 6, and Example 10 kept the same ratio of theplasticized PVOH to VISTAMAXX™ 1120 shown in Example 7.

EXAMPLE 11

A film was formed from the blend of Example 5 as described above.

EXAMPLE 12

The mechanical properties of the films of Examples 6-11 were tested asdescribed above. The results are shown in Table 1.

TABLE 1 Thermoplastic Film Mechanical Tensile Properties Peak FilmStress Elongation Modulus Thickness (MPa) (%) (MPa) Example SampleDescription Composition MD (mil) CD (mil) MD CD MD CD MD CD 6p-Elvanol/VM1120 60/40 2.4 2.3 26 16 359 266 86 83 7 p-Elvanol/VM112070/30 2.1 2.1 22 14 265 144 142 116 8 p-Elvanol/VM1120/Slip Agent60/40/1 2.1 1.9 24 13 341 250 63 58 9 p-Elvanol/VM1120/Slip 60/40/1/52.2 2.1 22 12 311 221 98 84 Agent/Fusabond MC190D 10p-Elvanol/VM1120/Slip 70/30/1/5 2.1 2.0 29 18 293 219 186 156Agent/Fusabond MC190D 11 p-Elvanol 85/15 1.1 1.0 48 46 173 161 1224 1554(Elvanol 51-05/Glycerin)

The modulus of the films without processing aids was low except forExample 7, indicating that the film was flexible and soft, these aredesired material properties for product applications. In comparison, theplasticized ELVANOL™ 51-05 film (without an thermoplastic elastomeradded) of Example 11 showed the highest modulus and peak stress,indicating a rigid film. With the presence of an elastomer in theblends, the film elongation was generally greater than that for theplasticized ELVANOL™ 51-05. Examples 8, 9, and 10 showed the effect ofusing a slip additive and compatibilizer in the blends. For example, thefilm elongation and peak stress slightly decreased when the slipadditive was used alone (Example 8) or with the compatibilizer (Example9). At the same level of the slip agent and compatiblizer, Example 10used less VISTAMAXX™ 1120 at 30%, which is 10% less than that in Example9. The film peak stress increased significantly with negligible decreasein the film elongation. Comparing Example 10 with Example 7, the peakstress increased 7 MPa (32%) in MD and 4 MPa (29% in CD); the elongationincreased from 265% to 293% in MD and from 144% to 219% in CD by adding1% slip and 5% compatibilizer.

EXAMPLE 13

The films of Examples 6-11 were subjected to the above-described waterdisintegration test. The results are set forth below in Table 2.

TABLE 2 Film Disintegration Time Time (min.) To First To 25 mm2 WaterTemp. Break pieces Run (° C.) RPM (min.) (sec.) (min.) (sec.) Example 6p-Elvanol/VM1120 (60/40) 1 23.6 26 N/A N/A N/A N/A 2 23.6 26 N/A N/A N/AN/A Example 7 p-Elvanol/VM1120 (70/30) 1 23.6 26 N/A N/A 4 42   2 23.626 N/A N/A 4 27   Example 8 p-Elvanol/VM1120 (60/40) with 1 23.6 26 N/AN/A N/A N/A 1% slip agent 2 23.6 26 N/A N/A N/A N/A Example 9p-Elvanol/VM1120 (60/40) with 1 23.6 26 N/A N/A N/A N/A 1% slip agentand 5% MC190D 2 23.6 26 N/A N/A N/A N/A Example 10 p-Elvanol/VM1120(70/30) with 1 23.6 26 0 18.00 0 18.00 1% slip agent and 5% MC190D 223.6 26 0 17.00 0 17.00 Example 11 p-Elvanol 1 23.6 26 0 13.00 0 40.00 223.6 26 0  7.00 0 25.00

The films of Examples 6, 8, and 9 did not disperse in water duringtesting and as such, the test was terminated after 30 minutes. Ingeneral, once the samples were placed in water, they started to changecolor. The film of Example 10 (with processing aids), for example,changed its color from clear to white once it was placed in water andfell apart in strings in less than one minute. Shortly thereafter, allof the strings clumped together. In contrast, the film of Example 7(without processing aids) took only about 5 minutes to disperse into twopieces.

EXAMPLE 14

To assess elasticity, the films of Examples 6-10 were subjected to cycletesting as described above. Example 14 in Table 4 was the film formedfrom 100% VISTAMAXX™ 1120 resin from ExxonMobil as described above.Before testing, the net gauge film length was 51 millimeters. Theresults are set forth below in Table 3.

TABLE 3 Film Mechanical Stretch and Recovery Testing After % Not ExampleSample Description Original After Test After 10 min 20 min After 30 minRecovered 6 p-Elvanol/VM1120 (60/40) - MD 51 71 61 60 60 17.6p-Elvanol/VM1120 (60/40) - CD 51 67 60 59 59 15.7 7 p-Elvanol/VM1120(70/30) - MD 51 73 55 54 54 5.9 p-Elvanol/VM1120 (70/30) - CD 51 BrokenBroken Broken Broken N/A 8 p-Elvanol/VM1120 (60/40) with 1% slip agent -MD 51 74 63 62 61 19.6 p-Elvanol/VM1120 (60/40) with 1% slip agent - CD51 68 60 59 58 13.7 9 p-Elvanol/VM1120 (60/40)1% slip agent and 5% 51 7865 64 63 23.5 MC190D - MD p-Elvanol/VM1120 (60/40) with 1% slip agentand 5% MC190D - CD 51 Broken Broken Broken Broken N/A 10p-Elvanol/VM1120 (70/30) with 1% slip agent and 51 85 68 66 66 29.4 5%MC190D - MD p-Elvanol/VM1120 (70/30) with 1% slip agent and 51 81 63 6363 23.5 5% MC190D - CD 14 VM 1120 (100%) - MD 51 55 54 54 54 5.9 VM 1120(100%) - CD 51 55 54 54 54 5.9

EXAMPLE 15

The melt viscosity for the starch-based material, plasticized Elvanol™51-05 and CelVol™ 523S was determined using a Gottfert Rhoegraph 2003capillary rheometer. The results are shown in FIG. 3. For comparativepurposes, a shear rate of 1000 s⁻¹ was also selected to calculate ratiosof the plasticized PVOH or starch-based blend to the Vistamaxx™ 1120.These values are tabulated in Table 4.

TABLE 4 The Ratio of Plasticized PVOH or Starch-Based Blend to ElastomerApparent Viscosity (Pa-S) Shear Rate Starch-Based (s⁻¹) Blend p-Celvol523S p-Elvanol 51-05 VM1120 1000 26   114    42   38   Example 1 Example2 Example 3 Example 7 Viscosity 0.7 3.0 3.0 1.1 Ratio

The preferred ratio for forming water-sensitive films was from 0.6 to2.5.

EXAMPLE 16

A scanning electron microscopy (SEM) photograph was taken of the film ofExamples 6 and 7. The photographs were obtained by plasmaetching/optical method using the standard secondary electron imagingmode achieved by a positive-biased Everhart-Thornley detector. Theresults are shown in FIG. 4 and 5, respectively. As indicated in FIG. 4,the film of Example 6 exhibited a laminar structure showing relativeincompatibility with continuous layers substantially parallel to thefilm surface. Such layers are believed to inhibit water access andreduce water sensitivity. On the other hand, the film of Example 7exhibited improved dispersion of the elastomer into the water-solublepolymer phase, which improves water access and thus increases the watersensitivity of the film.

While the invention has been described in detail with respect to thespecific embodiments thereof, it will be appreciated that those skilledin the art, upon attaining an understanding of the foregoing, mayreadily conceive of alterations to, variations of, and equivalents tothese embodiments. Accordingly, the scope of the present inventionshould be assessed as that of the appended claims and any equivalentsthereto.

1. A water-sensitive elastic film comprising: at least one water-solublepolymer, wherein the water-soluble polymer has a weight averagemolecular weight of from about 10,000 to about 150,000 grams per moleand a number average molecular weight of from about 1,000 to about80,000 grams per mole; at least one plasticizer, wherein the weightratio of the water-soluble polymer to the plasticizer is from about 1 toabout 50; and at least one olefinic elastomer, wherein the weight ratioof the water-soluble polymer to the olefinic elastomer is from about0.01 to about 3.0.
 2. The film of claim 1, wherein the water-solublepolymer includes vinyl pyrrolidone, hydroxyethyl acrylate ormethacrylate, hydroxypropyl acrylate or methacrylate, acrylic ormethacrylic acid, acrylic or methacrylic esters or vinyl pyridine,acrylamide, vinyl acetate, vinyl alcohol, ethylene oxide, or acombination thereof.
 3. The film of claim 1, wherein the water-solublepolymer includes a vinyl alcohol polymer.
 4. The film of claim 3,wherein the vinyl alcohol polymer has a degree of hydrolysis of fromabout 80 mole % to about 90 mole %.
 5. The film of claim 1, wherein thewater-soluble polymer has a weight average molecular weight of fromabout 30,000 to about 75,000 grams per mole and a number averagemolecular weight of from about 10,000 to about 40,000 grams per mole. 6.The film of claim 1, wherein the water-soluble polymer has a solutionviscosity of from about 50 to about 800 milliPascal seconds, asdetermined in a 4% aqueous solution at 20° C.
 7. The film of claim 1,wherein the water-soluble polymer has a solution viscosity of from about200 to about 600 milliPascal seconds, as determined in a 4% aqueoussolution at 20° C.
 8. The film of claim 1, wherein the ratio of the meltviscosity of the olefinic elastomer to the plasticized water-solublepolymer is from about 0.6 to about 2.5.
 9. The film of claim 1, whereinthe plasticizer includes a polyhydric alcohol.
 10. The film of claim 9,wherein the polyhydric alcohol includes a sugar alcohol.
 11. The film ofclaim 1, wherein the weight ratio of the water-soluble polymer to theplasticizer is from about 3 to about
 15. 12. The film of claim 1,wherein the plasticizer constitutes from about 1 wt. % to about 30 wt. %of the film and the water-soluble polymer constitutes from about 20 wt.% to about 90 wt. % of the film.
 13. The film of claim 1, wherein theolefinic elastomer is an ethylene/α-olefin copolymer, propylene/α-olefincopolymer, or a combination thereof.
 14. The film of claim 13, whereinthe olefinic elastomer is metallocene-catalyzed.
 15. The film of claim1, wherein the olefinic elastomeric is a styrene-olefin block copolymer.16. The film of claim 1, wherein the weight ratio of the water-solublepolymer to the olefinic elastomer is from about 1.0 to about 2.0. 17.The film of claim 1, wherein the olefinic elastomer constitutes fromabout 10 wt. % to about 70 wt. % of the film.
 18. The film of claim 1,wherein the film contains a slip additive.
 19. The film of claim 18,wherein the slip additive includes a fatty acid salt, fatty acid amide,or a combination thereof.
 20. The film of claim 1, wherein the filmcontains a compatabilizer.
 21. The film of claim 20, wherein thecompatabilizer includes a maleated polyolefin.
 22. The film of claim 1,further comprising a starch, biodegradable polyester, or combinationsthereof.
 23. A release liner comprising the film of claim 1 and arelease agent coated onto a surface thereof.
 24. An absorbent articlecomprising the film of claim 1, wherein the absorbent article comprisesa body portion that includes a liquid permeable topsheet, a generallyliquid impermeable backsheet, and an absorbent core positioned betweenthe backsheet and the topsheet.
 25. The absorbent article of claim 24,wherein the backsheet includes the film.
 26. A method for forming awater-sensitive elastic film, the method comprising: melt blending acomposition comprising at least one water-soluble polymer, wherein thewater-soluble polymer has a weight average molecular weight of fromabout 10,000 to about 150,000 grams per mole and a number averagemolecular weight of from about 1,000 to about 80,000 grams per mole; atleast one plasticizer, wherein the weight ratio of the water-solublepolymer to the plasticizer is from about 1 to about 50; and at least oneolefinic elastomer, wherein the weight ratio of the water-solublepolymer to the olefinic elastomer is from about 0.01 to about 3.0; andextruding the composition onto a surface to form a film.
 27. The methodof claim 26, wherein melt blending occurs at a temperature of from about80° C. to about 300° C.
 28. The method of claim 26, further comprisingstretching the film in the machine direction, the cross-machinedirection, or both.